Conventionally, a seal ring 100, as shown in FIG. 10, is known as a device for sealing an annular gap between two members which can rotate freely relative to each other in a hydraulic device or such like. FIG. 10 is a schematic cross-sectional view showing an attached state of the seal ring 100 according to the conventional technique.
The seal ring 100 is a substantially annular member, and seals an annular gap 400 between a housing 200 and a shaft 300 attached in a shaft hole 201 of the housing 200.
The seal ring 100 is attached into an annular groove 301 formed in the shaft 300 and is pressed toward the non-sealed fluid side A by oil pressure P acting from the sealed fluid side O. And then, the periphery 101 comes into close contact with the inner circumferential face of the shaft hole 201 in the housing 200, and the end face 102 on the non-sealed fluid side A comes into close contact with the side wall 302 (on the non-sealed fluid side A) of the annular groove 301 of the shaft 300. This restrains a leakage of oil, such as, lubricating oil from the sealed fluid side O to the non-sealed fluid side A.
Generally, such a seal ring 100 used in a hydraulic device is separated in one area of the circumference and has a shape with ends in order to improve its attachability. As the shape of a separating part S of the seal ring 100, a step cut as shown in FIG. 11 is known. FIG. 11 is a schematic perspective view of the configuration of the separating part S of the seal ring 100 in the conventional technique.
In the separating part S of the seal ring 100, a projection 103 is formed at one end, and a recess 104 is formed at the other end, which is used in combination with the projection 103. The separated ends of separating part S are connected by fitting the projection 103 into the recess 104, thereby forming the annular seal ring 100.
Formed in the fitting area of the separating part S are: sliding seal faces 105a and 105b slidable in the direction of the circumference, which are formed by the contacts between the side faces 103a and 103b of the projection 103 and the side faces 104a and 104b of the recess 104 respectively; and a gap 106 absorbable any change in the length of the circumference of the seal ring, which is formed between the leading-end face 103c of the projection 103 and the deepest part face 104c of the recess 104.
Accordingly, even if the length of the circumference of the seal ring 100 changes due to a temperature change, etc., the side faces 103a and 103b of the projection 103 and the side faces 104a and 104b of the recess 104, respectively, slide against each other in the direction of the circumference. Thereby, the separating part S is stretched or compressed in the direction of the circumference (in the direction of arrow in FIG. 10), thus is able to absorb any change in the length of the circumference of the seal ring 100.
In addition, even if the length of the circumference changes, the contacts between the side faces 103a and 103b of the projection 103 and the side faces 104 and 104b of the recess 104 (i.e., the formation of the sliding seal faces 105a and 105b) are maintained respectively. This prevents such a gap that might allow communication between the sealed fluid side O and the non-sealed fluid side A from being formed in the separating part S.
Such a seal ring 100 is attached using a tapering tool 107 as shown in FIG. 12. FIG. 12 is a schematic perspective view of the state of the seal ring 100 attached using the tapering tool 107 as shown in FIG. 12.
To attach the seal ring 100, the seal ring 100 with the separating part S closed (i.e., the recess and projection are snugly fitted together) is first fitted on the periphery of the small-diameter part 107a of the tapering tool 107. Then, the seal ring 100 is pushed further toward a large-diameter part 107b along a tapering periphery 107c, whose diameter gradually increases toward the large-diameter part 107b from the small-diameter part 107a, thereby increasing the diameter of the seal ring 100 such that the separating part S is opened. Subsequently, the seal ring 100 is caused to fall into the annular groove 301 in a shaft 300 from the large-diameter part 107b. Then, the separating part S is allowed to return to its closed state again by the elastic resiliency of the seal ring 100. Thus, the seal ring 100 is attached in the annular groove 301.
When the seal ring 100 is caused to fall into the annular groove 301 and then the separating part S returns to its original closed state from the open one, the projection 103 and recess 104 slide against each other by face-to-face contact (etc., sliding seal faces 105a and 105b). As a result, slide resistance between the recess and projection when fitting together increases, degrading the attachability of the seal ring 100.
That is, since the slide resistance is high, the separating part S may not return to its original fitting state with only the elastic resiliency of the seal ring 100, ends up requiring an additional task for returning the separating part S to its original fitting state.
If the task for returning the separating part S to its original fitting state is inadequate, the seal ring 100 may be fitted to the housing 200, with the separating part S fitting inadequately. For example, the leading end side of the side face 104b extending concentric to the axis of the recess 104 may push the projection 103 upward in the direction of the outer circumference, with the result that a part of the projection 103 juts out toward the outer circumferential side, as shown in FIG. 13; and the seal ring 100 may be fitted to the housing 200, with the separating part S abnormally deformed. Such a jutting portion may interfere with the housing 200 during the fitting of the shaft 300 to the housing 200 and cause, for example, damage to the seal ring 100.
In addition, if the projection 103 and recess 104 do not slide against each other smoothly, stretching of the separating part S in the direction of the circumference may be impeded when the seal ring 100 is subject to oil pressure and is stretched in the direction of the outside diameter (i.e., when the seal ring 100 is pressed against the inner circumferential face of the shaft hole 201 of the housing 200). There is a concern that this may make the position of the seal ring 100 unstable and affect sealability.